Process fob separating acidic gases



Sept. 26, 1933. I R R BQTTOMS Re. 18,958

PROCESS FOR SEPARATING AC IDIC GASES Original Filed Oct. 7, 1930 I -if 10- 23 f L -15 E 5 7 ?0i \L JJ'- L 14 f! INVENTOR Koberi Kaye/30230;

BY M 4 gm 75- ATTORNEYS Reissued Sept. 26,. 1933 Robert Roger Bottoms, Louisville, Ky., assignor to The Girdler Corporation, corporation (it Delaware Louisville, Ky :1.

. 13 Claims.

This application is a substitution for and continuation in part of my prior. allowed application Serial No. 323,723, filed Dec. 4, 1928, allowed Sept. 26, 1930.

This invention relates to the separation of acidic'gases from other gases or gaseous mixtures, by means of an absorbent agent. By the term acidic gases" I mean those gases which in water solution have an acid reaction, but which are released unchanged upon sufiicient heating of the water. Carbon dioxide, sulphur dioxide and hydrogen. sulphide are the main gases of this type which are present in the gaseous mixtures commonly encountered in industrial operations.

The process may be employed for the separation and recovery of these acidic gasesfrom-the mixture, or may be employed to purify other gases by removal of said acidic gases therefrom.

The main objects of my invention are to facilitate the separation, effect complete or more nearly complete removal or recovery of said acidic gases, facilitate the regeneration of the absorbent agent, and toincrease the rate of such regeneration. To secure these objects I employ an absorbent agent which, in comparison with the usual alkaline carbonates, such as sodium treatment of a given volume of gas.

carbonate, has greater solubility and greater absorption capacity per unit of volume, whereby a smaller amount of the absorbent is needed and smaller and cheaper apparatus required for the I employ an absorbent agent which produces products with the acidic gases which are highly soluble and readily decomposed upon heating.

I have discovered that certain organic nitrogen compounds of the class known as amines may be employed for this purpose. An amine may be considered as an ammonia substitution compound in which one or more of the hydrogen,

known prior to my invention that certain compounds forming a comparatively small group of the amines possessed,the properties of chemically uniting with acidic gases at a comparatively low temperature range, giving up the gas in gaseous form at a higher temperature and at the same time becoming regenerated, and having a low vapor pressure during the absorption stage and also during the heating or gas liberating stage. The possession of these properties permits the absorption agent in liquid form to be circulated continuously in a closed cycle through the low temperature absorption and higher temperature regeneration stage, with comparatively slight loss of the absorbent agent, long life for the absorbent agent in circulation, minimizing of heat consumption through the use of heat interchang'ers, and the treatment 'of large volumes of gases for comparatively small volumes of the absorbent.

I have furthermore discovered that these properties are possessed only by these amines whichv have certain chemical characteristics as to arrangement of atoms and certain physical characteristics. The presence ,of 'oxygen in addition to nitrogen and hydrogen is not objectionable, but the oxygen must not be present in a carboxyl (COOH) group or a'carbonyl (CO) group, although it may be present in a hydroxyl (OH) group. The amine must be either solid or liquid atv ordinary room temperature, and must have a boiling point not substantially below 100 C. It must be soluble in water or other liquid which does not form a stable compound with the acidic gas or other gases associated therewith, and which has a boiling point not below the temperature of effective gas elimination.

The amines may be either primary, seco nd-, ary to .tertiary depending upon the number of hydrogen atoms of the ammonia which are replaced by carbon containing groups, and they may be either mono, di or tri-amines depending upon the number of the amino groups involved.

The compound may contain an aliphatic amine group, that is, it may be an aliphatic amine in which the hydrocarbon group may comprise merely a straight chain which may be saturated orunsaturated, or an aliphatic group with an attached ring which may be saturated or unsaturated.

By the term aliphatic amine or aliphatic amino group I mean a compound in which the amino group (NHz) is attached to a methylene 105 group (CH3). The methylene group may be attached to one or more aliphatic or straight chain groups, or may be attached to a saturated or unsaturated ring.

The --following are examples of the aliphatic no amino compounds which have the chemical and physical characteristics above referred to and which are useful in my process. I may use a primary monoamine, such as hexylamine, or a secondary monoamine, such as dipropylamine. Of the diamines I may employ propylene diamine or a tertiary diamine, such as trimethylene diamine. A triamine which may be employed is triaminopropane. Of the compounds which include an aliphatic amino group having a hydroxyl group I may employ monoethanolamine (amino ethyl alcohol), diethanolamine, trlethanolamlne, dihydroxypropylamine (glyceroamine), or dietlrylaminoethyl alcohol.

All of these have an aliphatic amino group, are all saturated compounds, all have a boiling point above 0., are all soluble in water, and they are either primary, secondary or tertiary, and either mono, di or tri-amines. None has a carboxyl or carbonyl group.

Of the aliphatic amines without ring compounds, but with hydroxyl groups, it is advantageous to use triethanolarnine instead of either of the other two ethanolamines, namely, diethanolamine or monoethanolamine alone, because it has the higher boiling point, although triethanolamine as commercially manufactured and without careful purification, contains certain amounts of both the diethanolamine and the monoethanolamine. In referring to triethanolamine I therefore mean this compound either of ordinary purity or in its pure state in water solution.

As an example of an unsaturated aliphatic amine I may employ pentallyl dimethylamine.

As an example of an aliphatic amine of the type known as an alphyl amine and which has a carbon ring attached to the aliphatic amino group, I may employ benzylamine, phenylethylamine or methylphenylmethylamine.

Of the aliphatic amines in which there is a saturated or unsaturated ring attached to the aliphatic amino group, it is advantageous to use the benzylamine, because of its simplicity and cheapness of manufacture and the fact .that it will absorb more of the acidic gas per unit of weight.

Aliphatic amines do not include compounds in which a separate unsaturated ring is the only group directly connected to the amino (NHz) group. For instance, aniline is not useful in my process.

The nitrogen of the aliphatic amino group may be a member of a heterocyclic ring, but

as the nitrogen of the amino group is attachedto the carbon of an aliphatic group, these compounds may be properly classified as aliphatic amino compounds. Of such heterocyclic compounds having an aliphatic amino group are nicotine, piperidyl ethanol, piperidyl ethane, and pyrroline ethane. None of these compounds has a carbonyl or carboxyl group, although the piperidyl ethanol has a hydroxyl group. Of these compounds it is advantageous to use piperidyl ethanol.

Of the aliphatic amines which contain neither ring nor hydroxyl group it is most advantageous to use tripropylamine. A

I may employ an amine in which the ring is directly connected to the amino group, but only in case the ring be saturated. To this group belong the amines of the cycloparafllns, such as cyclohexylamine, cthylcyclohexylamine, tetrahydro-ortho-toluldine, and cyclopentylamine. These cycloparamn amines are all saturated compounds,

' contain no carbonyl or carboxyl groups, and have the desired physical characteristics. Of the naphthene or cycloparaflin amines which do not contain an aliphatic group, but which contain a saturated ring, it is advantageous to use cycloheiwlamine, although it will 'not absorb as much of the acidic gas as will triethanolamine because of the dissociation pressure of the produced compound which is higher. It has a lower molecular weight than the other two mentioned and absorbs more of the acidic gas per unit of volume than the other two.

I may also include certain hydrazines having the desired chemical and physical characteristics. These may be considered as amines in whlchone of the hydrogen atoms of the amino group (NHz) is replaced by another NH: group. For instance, I may use ethylhydrazine or propylhydrazine which have an amino group attached to an aliphatic group and therefore properly designated as aliphatic amines.

In my copending application Serial No. 488,740, filed Oct. 15, 1930, I have claimed broadly the process of separating acidic gases by the use of a certain class of hydrazines including thofi above mentioned, and have more specifically claimed the use of certain hydrazines which do some other liquid as the solvent and which does a not have a boiling point below 100 C. For instance, as the solvent I may employ tetrahydronaphthalene which in itself does not chemically unite with the acidic gases.

All of the compounds above referred to will unite with acidic gases to form compounds which are comparatively stable and have a very low vapor pressure or dissociation pressure at atmospheric temperature and pressure. Allsuch produced compounds are broken down by heat with the liberation of the acidic gas and the regeneration of the absorbent agent.

The compounds resulting from the chemical reaction with the acidic gases are comparatively unstable in a higher temperature range, for iribe initially formed and thereafter serve as the absorbent for further carbon dioxide inthe formation of a bicarbonate.

In all of these compounds the dissociation at the higher temperature results in the liberation of the acidic gas in gaseous form and the ,regeneration of the absorbent agent suitable for use in the absorption of further gas when cooled to the lower temperature.

As previously indicated, it is highly advantageous to use triethanolamine. This may be a viscous liquid, or in solution, for instance in water. I have discovered that this compound recovery of the carbon dioxide, sulphur dioxide or hydrogen sulphide or other acidic gases, has high viscosity which is conducive to a higher rate of absorption, may be regenerated ata comparatively high rate with minimum loss at steam temperature, and during regeneration gives up all or substantially all of the absorbed gas or gases. The compound is not caustic, and therefore is not harmful to use, and may be employed in processing equipment of ordinary materials."

The removal of the gas is by actual chemical combination, and the regeneration restores the compound to its original form and composition. This absorbent agent is not decomposed at the temperature of regeneration does not react with other gases ordinarily present in the industrial gases to be treated, has no objectionable odor, and does not impart any odor to the'gases separated at the higher temperature-or'the stripped gases at the lower temperature. l

The compounds which are formed with the acidic gases are comparatively stable at atmospheric temperature and the instability increases as the temperature rises, substantially all of the acidic gas being driven ofi at the boiling temperature of the liquid. The extent to which the absorbent agent is regenerated may vary in commercial practice depending upon the temperature in the regenerator and the time that the liquor is maintained in the high temperature range of the cycle.

The process may be carried out in various types 01! apparatus, and intermittently or continuously. In the accompanying drawing the single figure shows diagrammatically a vertical section through a form of apparatus which may be employed for a continuous process.

In this apparatus there is employed an absorber 10 which is preferably in the form of a column of suitable height and provided with bailies, pebbles, or other suitable filler, to effect reduced rate of flow and eificient contact of the down-flowing liquid and the up-flowing gas. Within the absorber is the absorbing agent, preferably triethanolamine in water solution. The absorbing agent is continuously delivered to the top of the absorber through a pipe 11, while the gas to be treated is delivered to the lower part through a pipe 12. The stripped gas is taken off from the top of the column through a pipe 13, while the absorbent, with the absorbed gases, is taken off from the bottom through a pipe 14.

In connection with the absorber .there is employed a regenerator .15 which has suitable means for efiecting intimate contact of the downilowing absorbent agent carrying the absorbed gas and the up-flowing gas separated from the absorbent. agent in the regenerator. The absorbent, carrying the absorbed gas, is conducted from the pipe 14 through a pipe 16, to the top of the regenerator, by means of a pump 17. In the bottom of the regenerator is a heating means, such for instance as a steam coil 18. The gas driven off from the absorbent agent in the regenerator is taken off from the top of the regenerator through a pipe 19, while a pump 20 withdraws the regenerated absorbent through a pipe 21 from the bottom of the regenerator and condenser at the top of the regenerator.

delivers it to the pipe 11 which leads to the top oi the absorber. It is necessary that the temperature of the regenerator be higher than in the absorber.

cool the liquiddelivered through the pipe 11. This may be accomplished by any suitable form of heat interchanger 22. The liquid flowing from the bottom of the regenerator through the pipe 12 flows through this heat interchanger in one direction, while the saturated absorbent from the bottom of the absorption column passes through the heat interchanger in the opposite direction to the upper part of the regenerator. The

pipe 11 between the bottom of the heat interchanger and the top of the absorption column may be provided with an additional cooler 23.

In carrying out the process, the gas to be treated is delivered through the pipe 12, and passes up through the absorber. The carbon dioxide, sulphur dioxide, or hydrogen sulphide, is

removed by the action of the triethanolamine, and the stripped gas passes out the pipe 13. The triethanolamine with the absorbed gas is removed through the pipe 14, heated by the heater 18 and interchanger 22, and delivered near the top of the regenerator. Within the latter apparatus, the

Thus it is desirable to heat the. liquid delivered through the pipe 16 and to-- liquid trickles down through to the bottom and gives up the absorbed gas which later escapes through the pipe 19. A further portion of the absorbed gas is removed by the heating coil 18,

and the regenerated absorbent is cooled-in the heat interchanger 22 and cooler 23 and returned for reuse in the absorber. Thus the process is a continuous one.

In some cases or with some absorbent agents the liquid in the regenerator may be heated to such a temperature that a small portion of the solvent 1 or the organic nitrogen compoundmay be vaporized. To prevent loss it is preferable to add a I have shown somewhat conventionally a condenser 24 in which a cooling liquid, such as water, is circulated around a series of pipes between a supply pipe 25 and an outlet pipe 26. The cooled acidic gases leave the condenser through a pipe 27, while all condensate comprising either the solvent or the organic nitrogen compound-or both is returned through a trap-28 to the top of the regenerator.

My improved process may be employed for treating a wide variety of gases. Merely as an example, stack gases may be treated for the recovery of the carbon dioxide contained therein, or gases from roasting furnaces may be treated to recover sulphur dioxide. In both such cases the treatment is for the recovery of the valuable constituents of waste gases. may be used in treating natural gas, city gas,

refinery gas, water gas or-hydrogen, for the re- On the other hand, it

gases treated and render them better suited for the purposes for which they are to be employed.

Carbon dioxide may be removed from natural gas-preparatory to extracting helium from the latter, or carbon dioxide may be removed from air preparatory to liquefaction of/the latter and extractionof the oxygen. Where hydrogen is produced from coke, thishydrogen may be treated ent in appreciable quantities and constitutes a very undesirable impurity of the hydrogen.

It will, of course, be obvious that the apparatus referred to is merely conventionally illustrated to'remove such hydrogen sulphide as is often prestion as the absorbing agent, steam serves as a suitable heating agent in the heating coil 18, while water of ordinary temperature may be employed in the cooler. 23 and condenser 24. In some cases, andparticularly with some other amino compounds, it may be desirable to heat to a higher temperature by means of superheated steam, and cool to a lower temperature by the action or brine, while with others less heating and less. cooling is required. Withtriethanolamine no excessive heating or cooling action is required.

Due to the high rate of absorption and the high rate of regeneration, the columns of the absorber and regenerator maybe made very much shorter than is possible when other materials such as alkalies or carbonates are used as the absorbing agents. Substantially complete regeneration may be obtained without either vigorous boiling or blowing with air, as isnow required with some 30 absorbing agents.

In my improved process it is neither necessary nor desirable to use any inorganic bases. Such bases may in some cases havea very deleterious effect upon the amine employed. In some cases the presence of a small amount 01 sodium carbonate or other such inorganic compound might not do any harm, but the addition would not, so far. as I know, serve any useful p p se.

Having thus described my invention, what-I claim as new and desire to secure by Letters Patent is:

1. The process of separating an acidic'gas from gaseous mixtures, which includes'eifecti'ng intimate contact of a gaseous mixture with an absorbent agent in liquid form which will liberate the acidic gas upon subsequent treatment and become regenerated and which includes an amine selected from the group consisting of aliphatic and cycloparaflin amines, and which is free from carboxyl or carbonyl groups, and which has a boiling point, not substantially below 100' C., and .thereafter treating'said absorbent to sepanatethe absorbed gas and regenerate the absorbent.

2. The process of separating acidic gases from gaseous mixtureawhich includes effecting intimate contact of the gaseous mixture with anabsorbent in liquid form which will liberate the acidic gas upon subsequent treatment and become regenerated and which includes an aliphatic amine which is free of carboxyl and carbonyl groups, and which has a boiling point not substantially below 100 C.', and thereafter treating said absorbent to separate the absorbed gas and regenerate the absorbent.

3. The process of separating acidic gasesfrom gaseous mixtures, which includes efl'ecting intimate contact of the gaseous mixture with an absorbent in liquid form which will liberate the 70 acidic gas upon subsequent treatment and become regenerated andwhich includes an amino alcohol which has a boiling point not substantially below 100 C., and thereafter treating said absorbent to separate the absorbed gas and regenerate the absorbent.

4. The process of separating acidic gases from gaseous mixtures, which includes eflectlng' intimate contact of the gaseous mixture with an ab sorbent in liquid form which will liberate the acidic gas upon subsequent treatment andbecome regenerated and. which includes an allphatic amino alcohol which has a boiling point not substantially below 100 C., and thereafter treating said absorbent to separate the absorbed gas and regenerate the absorbent. v

5. The process of separating acidic gases from 4 gaseous mixtures, which includes eifecting intimate contact of the gaseous mxiture with an absorbent in liquid'form including an ethanolamine which has a boiling point not substantially below 100 C., and thereafter treating said absorbent toseparate the absorbed gas and regenerate the absorbent. 6. The process of separating carbon dioxide, sulphur dioxide or hydrogen sulphide, or other acidic gases from gaseous mixtures, which includes eflecti'ng intimate contact of the gaseous mixture with triethanolamine, and thereafter treating the resulting product to separate the absorbed gas andregenerate the triethanolamlne;

'7. The process of separating acidic gases from gaseous mixtures, which includes effecting intimate contact of the gaseous mixture with an absorbent agent including triethanolamine, and thereafter heating said absorbent agent to separate therefrom the absorbed gases. 7

8. The process of treating a gaseous mixture, including carbon dioxide, sulphur dioxide, hydrogen sulphide, or other acidic gases, which includes circulating a water solution of triethanolamine in a closed cycle, passing the gaseous mixture to be treated in contact with said solution at one point in the cycle and heating the solution to remolre the absorbed gases at another point in the cyc e. I

9. The process of separating acidic gases from gaseous mixtures, which includes effecting intimate contact of the gaseous mixture with an absorbent in liquid form which will liberate the acidic gas upon subsequent treatment and become regenerated and which includes a'cycloparaflin amine which is free of carboxyl and carbonyl groups, and which has a boiling'point not sub* stantially below 100 0., and thereafter treating 1% said absorbent to separate the absorbed gas and regenerate the absorbent. l

' 10. The process'of separating acidic gases from gaseous mixtures, which includes eifecting intimate contact of the gaseous mixture with an absorbent in liquid form including cyclohexylamine, and thereafter treating said absorbent to separate the absorbed gas and regenerate the absorbent.

11. The process of separating acidic gases from gaseous mixtures, which includes efiecting intimate contact of the gaseous mixture with an absorbent in liquid form which will liberate the 'acidic gas upon subsequent treatment and become regenerated and which includes a tertiary 4 heterocyclic amine which is free of carboxyl and carbonyl groups, and which has a boiling point not substantially below 100 (2., and thereafter v treating said absorbent to separate the absorbed gas and regenerate the absorbent.

Y 12. The process of separating acidic gases from gaseous mixtures, which includes effecting intimate contact 01' the gaseous mixture with an absorbent in liquid form which will liberate the acidic gas upon subsequent treatment and become regenerated and which includes a tertiary heterocyclic amino alcohol which has a boiling point not substantially below 0., and thereafter treating said absorbent to separate the absorbed gas and regenerate the absorbent.

13. The process of separating acidic gasesfrom gaseous mixtures, which includes efl'ecting inti-' 

